The present invention relates to a cylinder injection type internal combustion engine in which fuel is injected directly into a combustion chamber of an internal combustion engine, a control method for an internal combustion engine, and a fuel injection valve.
In a conventional internal combustion engine of this type, a projecting portion is formed in the center on top face of a piston to form a depression called a cavity in the piston. Thereupon, fuel is injected from a fuel injection valve toward this cavity in the piston at the second half stage of the compression stroke of the internal combustion engine, so that a fuel spray repelled by the cavity is concentrated in the direction of ignition plug (Society of Automotive Engineers of Japan Annual Proceedings 976, Paper No. 9740307, October, 1997).
Thus, the stratification of fuel in the combustion chamber is achieved, and combustion can be produced even with a lean mixture of an air-fuel ratio of about 40. Usually, such a combustion process is referred to as a stratified charge lean burn operation, which serves for reducing fuel consumption at the time of low-load operation of the internal combustion engine.
Also, JP-A-7-119507 has disclosed a combustion system in which at the time of high-load operation, the operation is switched to a so-called homogeneous operation in which fuel is injected during the intake stroke so that the fuel is distributed uniformly in the whole of the combustion chamber.
Further, JP-A-6-81656, JP-A-10-110660, JP-A-7-293259, JP-A-10-30441, JP-A-10-169447, and JP-A-10-896, and U.S. Pat. No. 5,850,816 have disclosed a combustion, system in which a tumble air flow is produced in the combustion chamber, and a fuel spray is concentrated around the ignition plug by this tumble air flow.
However, even if any of the above-described combustion systems is used, most of fuel injected from the injection valve sticks to the piston and the wall surface in the combustion chamber, so that there are limitations in increasing fuel efficiency and reducing harmful components (for example, hydrocarbon) in exhaust gas due to the stratified charge operation.
Also, the stratified charge operation cannot be provided under a condition of 80 km/h or 2400 rpm and higher.
A first object of the present invention is to reduce fuel sticking to the piston and the wall surface in the combustion chamber and to decrease HC in exhaust gas.
A second object of the present invention is to increase the output at the time of homogeneous operation.
A third object of the present invention is to provide a fuel injection valve for cylinder injection, in which less fuel sticks to the piston.
A fourth object of the present invention is to enable the stratified charge operation even at a vehicle speed of 80 km/h and higher or at an engine rotational speed of 2400 rpm and higher (for example, in a high speed region where the vehicle speed is 120 km/h or the engine rotational speed is 3200 rpm).
The above first object is attained by a cylinder injection type internal combustion engine comprising a combustion chamber into which air is sucked; a fuel injection valve for injecting fuel directly into the combustion chamber; and a piston for changing the volume of the combustion chamber, whose central portion of top face is equal in height to or lower than the surroundings, characterized in that a stratum of the sucked air or a stratum of air flow is interposed between a fuel spray injected from the fuel injection valve and the piston.
Also, the above first object is attained by a cylinder injection type internal combustion engine comprising a fuel injection valve for injecting fuel directly into a combustion chamber of the internal combustion engine, characterized in that penetration of a fuel spray injected from the fuel injection valve into the combustion chamber is set to be shorter than a distance between the top face of a piston reciprocating in the combustion chamber and a fuel discharge port of the fuel injection valve during a period of time from the start of injection to the completion of injection of fuel.
Also, the above first object is attained by a cylinder injection type internal combustion engine comprising a fuel injection valve for injecting fuel directly into a combustion chamber of the internal combustion engine, the fuel injection valve being formed so that the penetration of a fuel spray 3.8 msec after the injection of fuel to the atmosphere of the atmospheric pressure is 60 mm or shorter.
Also, the above first object is attained by a cylinder injection type internal combustion engine comprising a fuel injection valve for injecting fuel directly into a combustion chamber of the internal combustion engine, the fuel injection valve being formed so that a fuel spray with a Zauter mean particle size of 20 xcexcm or smaller is injected.
Also, the above first object is attained by a cylinder injection type internal combustion engine, comprising a combustion chamber for the internal combustion engine into which air is sucked through an intake valve; a fuel injection valve for injecting fuel directly into the combustion chamber; swirl flow generating means for generating an air flow in the combustion chamber; and operation condition detecting means for detecting the operation condition of the internal combustion engine, the internal combustion engine having a control unit for supplying a fuel injection valve driving signal to the fuel injection valve so that fuel is injected at the second half stage of the compression stroke when the detected operation condition is at a low load.
Also, the above second object is attained by a cylinder injection type internal combustion engine comprising a combustion chamber of the internal combustion engine, into which air is sucked through an intake valve; a fuel injection valve for injecting fuel directly into the combustion chamber; swirl flow generating means for generating a swirl air flow in the combustion chamber; and operation condition detecting means for detecting the operation condition of the internal combustion engine, the internal combustion engine having a control unit for supplying a fuel injection valve driving signal to the fuel injection valve so that fuel is injected on the intake stroke when the detected operation condition is at a medium load.
Also, the above second object is attained by a cylinder injection type internal combustion engine comprising a combustion chamber of the internal combustion engine, into which air is sucked through an intake valve; a fuel injection valve for injecting fuel directly into the combustion chamber; and operation condition detecting means for detecting the operation condition of the internal combustion engine, the internal combustion engine having a control unit for supplying a fuel injection valve driving signal to the fuel injection valve so that fuel is injected for a period of time when the intake air velocity is lower than the spray velocity on the intake stroke when the detected operation condition is at a high load.
Also, the above second object is attained by a cylinder injection type internal combustion engine comprising an upstream swirl type fuel injection valve for injecting fuel directly into a combustion chamber of the internal combustion engine; and operation condition detecting means for detecting the operation condition of the internal combustion engine, the internal combustion engine having a control unit for supplying a fuel injection valve driving signal to the fuel injection valve so that fuel is injected at a time for a period of time when the intake air velocity is higher than the spray velocity on the intake stroke when the detected operation condition is at a high load.
Also, the above first object is attained by a control method for a cylinder injection type internal combustion engine, in which when the operation condition of the internal combustion engine is at a low load, a swirl air flow is generated in a combustion chamber, fuel is injected at the first half stage of the compression stroke, and a rich mixture stratum is formed inside the swirl air flow, whereby stratified charge lean operation is performed.
Also, the above second object is attained by a control method for a cylinder injection type internal combustion engine, in which when the operation condition of the internal combustion engine is at a medium load, a swirl air flow is generated in a combustion chamber, fuel is injected on the intake stroke, and a mixture with a homogeneous concentration is generated in the combustion chamber by the swirl air flow, whereby homogeneous lean operation is performed.
Also, the above second object is attained by a control method for a cylinder injection type internal combustion engine, in which when the operation condition of the internal combustion engine is at a high load, fuel having an amount capable of achieving a stoichiometric air-fuel ratio is injected for a period of time when the intake air velocity is lower than the spray velocity on the intake stroke, and a mixture with a homogeneous concentration is generated in the combustion chamber by intake air, whereby homogeneous stoichiometric operation is performed.
Also, the above third object is attained by a fuel injection valve for injecting fuel directly into a combustion chamber of an internal combustion engine, characterized in that a fuel spray injected from the fuel injection valve has a penetration of 60 mm or shorter 3.8 msec after the time when fuel is injected to the atmosphere of the atmospheric pressure.
Also, the above third object is attained by a fuel injection valve for injecting fuel directly into a combustion chamber of an internal combustion engine, characterized in that the spray particle size of fuel injected from the fuel injection valve is 20 xcexcm or smaller in terms of Zauter mean particle size.
Further, the above fourth object is attained by a cylinder injection type internal combustion engine comprising a combustion chamber into which air is sucked; a fuel injection valve for injecting fuel directly into the combustion chamber; and a piston for changing the volume of the combustion chamber, characterized in that an air flow is generated in the combustion chamber to form a stratum of the sucked air or a stratum of air flow between a fuel spray injected from the fuel injection valve and the piston, and a guide face for guiding the flow on the top face of piston to a position just under the injection valve.
Specifically, the object is attained by a cylinder injection type internal combustion engine comprising air flow generating means for generating a tumble air flow in a combustion chamber of the engine; a piston having a top face shape contrived so as to guide the air flow generated in the combustion chamber from the side distant from a fuel injection valve to a position just under the fuel injection valve along the top face of the piston; and the fuel injection valve for supplying a fuel spray to the outer stratum of the air flow extending from the fuel injection valve to an ignition plug.